Large study finds association between soft drinks and diabetes, but a U of M researcher isn’t so convinced — yet

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A meta-analysis of 11 different studies has found that regularly drinking sugar-sweetened soda or other beverages significantly increases people’s relative risk of type 2 diabetes and metabolic syndrome.

And, apparently, you don’t have to drink much of the stuff to raise your risk. The Harvard School of Public Health researchers who conducted the meta-analysis found that people who daily down a single 12-ounce serving of a sugar-sweetened beverage increase their chances of developing type 2 diabetes by 15 percent compared to those who consume less than one sugary drink a month.

Make that two servings and the relative risk increases to 26 percent for diabetes and to 20 percent for metabolic syndrome. (Metabolic syndrome is not an illness, but a group of risk factors, such as high blood pressure and extra body fat around the abdomen, that are believed to put people at increased risk of such illnesses as diabetes and heart disease.)

Right now, about 1 in 10 Americans have diabetes. A 26 percent increase in risk alters those odds to about 1 in 8. (The Centers for Disease Control and Prevention released a report last week that projected that 1 in 3 Americans will have type 2 diabetes by 2050, if current trends continue.)

For the meta-analysis, which appears in the November issue of the medical journal Diabetes Care, sugary drinks were defined as soft drinks, fruitades, fruit drinks (but not 100 percent fruit juices), sports drinks, energy and vitamin water drinks, sweetened ice tea, punch, cordials, squashes and lemonade. Such beverages are now the primary source of added sugars in the U.S. diet.

The meta-analysis demonstrated, say its authors, “that higher consumption of [sugar-sweetened beverages] is significantly associated with development of metabolic syndrome and type 2 diabetes. It provides further support to limit consumption of these beverages in place of healthy alternatives such as water to reduce obesity-related chronic disease risk.”

Wanted: more evidenceTo get another opinion on these findings, I called Mark Pereira, an associate professor in epidemiology and community health at the University of Minnesota’s School of Public Health. One of his studies was among the 11 included in the meta-analysis. And earlier this year, Pereira published a study that found that drinking two or more soft drinks per week increased the relative risk of pancreatic cancer by 87 percent.

“Their conclusions are more or less definitive, but to me, [a causative link between soft drinks and diabetes] is really up in the air due to the limitation of the research and the lack of experimental studies,” he said.

Pereira pointed out that the studies used in the meta-analysis are all observational ones. In other words, they can show only an association between two things (in this case sugary drinks and diabetes and metabolic syndrome), not cause and effect.

Observational studies are fraught with problems. To begin with, such studies use self-reported food frequency questionnaires that can be riddled with errors. People may misjudge how much or often they eat or drink a particular food, or they may not understand what they’re eating or drinking. (How many people understand the difference between “fruit drink” and fruit juice?)

In addition, he said, “if you’re going to study soft drinks and try to approximate the effect they’re going to have on diabetes risk, you have to include all the other potential sources in the diet that might bias or confound the findings.”

Although the 11 studies tried to account for confounding factors, such as smoking, physical activity, body mass index (BMI) and other food choices, they couldn’t catch all of them. For example, only three of the studies in the meta-analysis took into account other beverages. “That’s really important because if you drink a lot of soda, you’re probably drinking a lot less milk and fruit juice,” said Pereira.

In other words, is it the soda that’s causing the diabetes, or is it the lack of nutrients from other food sources that are displaced by the soda that leads to diabetes and other health problems?

The meta-analysis’ findings “could be really important,” he added, “but we need a better study.”

Pereira and his colleagues at the University of Minnesota are currently seeking funding for a controlled clinical trial to determine the precise long-term physiological effects of sugar-sweetened beverages on the body.

In the meantime, though, Pereira agrees with the authors of the meta-analysis that consumers would be wise to limit their consumption of soft drinks and other sugary beverages.

“The fundamental principles of nutrition would tell you to be careful about how many soft drinks you consume,” he said. “The more you consume, the lower the nutrient density of your diet. You’re increasing your calories and not getting any nutrients at all.”